A conventional magnetic tape drive library system includes a number of tape drive slots; a number of magnetic tape cartridge magazine slots; and a tape cartridge elevator positioned intermediate the tape drive slots and the magnetic tape cartridge magazine slots. The elevator is linearly movable along a guide shaft and may be actuated by a motor for positioning the elevator adjacent to either a magazine slot or a tape drive slot. Further, the elevator includes a mechanism for engaging a tape cartridge; extracting the tape cartridge from the magazine slot and for inserting the tape cartridge into a targeted tape drive. After completion of data processing operations with a particular tape cartridge, the elevator mechanism will again engage the tape cartridge and transport the cartridge back to its original magazine slot.
In this aspect, the tape drive library system further includes a housing having one side wall adapted for receiving the number of tape cartridge magazines, and another side wall adapted for receiving the number of tape drives. The tape cartridge magazines are typically loaded with a plurality of tape cartridges prior to being introduced to the library system.
An external host computer controller is connected to the tape library system for controlling data processing operations during use of the system. The host computer controller issues commands to a microcontroller that is preprogrammed with a media changer command control set. The command set essentially controls functional operations of the tape library system, such as: selecting and loading a tape cartridge, as well as formatting, locating, overwriting, erasing, and reading/writing data on the magnetic storage tape within the tape cartridge.
One drawback of conventional mechanized tape library systems is the relatively long response time to a request for data. The long response time is principally attributed to the inherent mechanical latencies defined within the system. The mechanical latencies involved in a request for data are derived from the steps the library system must follow in order to fulfill the data request, such as, moving an elevator to a tape cartridge magazine slot and physically extracting the cartridge. Thereafter the elevator must move the cartridge to a targeted tape drive and after loading the cartridge into the tape drive, the drive must spool the tape to the appropriate storage location of the sought after data stored on the tape. Because of such data transfer latencies, tape library system applications have been limited to archival storage/retrieval applications for a relatively large number of faster input/output data processing systems such as disk drives or solid state electronic storage devices.
Another drawback of tape library systems is directed to the under utilization of the storage capacity of the tape cartridges within the tape library system. More precisely, since conventional tape cartridges require sequential data access, a conventional tape library system inherently requires substantial system resources to store/retrieve many different types of user data on a single tape cartridge or to split user data between the tail end of one cartridge and the beginning of another cartridge. Therefore, tape library systems may store a single type of user data on a single tape cartridge and simply begin storage of another type of user data on a subsequent tape cartridge regardless of whether the former tape cartridge is full. This significantly under utilizes the storage capacity of a tape library system.
Thus, a hitherto unsolved need has remained for a simplified magnetic tape drive library system with increased data access rates that may make substantial use of current control microcode, e.g., media changer command control sets. Further, a need has remained for a simplified magnetic tape drive library system that fully uses the storage capacity of a tape cartridge.